Atomic and molecular interstellar medium in high redshift star-forming galaxies

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Galaxies are the fundamental structural building blocks of the observable Universe. They contain the stars (and planets) together with the multi-phased, hot and cold, atomic and molecular interstellar medium (ISM) from which the stars themselves formed. Recent developments in observing technology for near-infrared and millimeter-wave imaging-spectroscopy have enabled breakthrough studies of the cosmologically cooled ISM in young high-redshift star-forming galaxies (SFGs). This includes the critical epochs when most of the mass was assembled in galaxies, through the rise, peak, and decline in the global cosmic star-formation rate. The molecular ISM is expecially important for the study of galaxy evolution because this material is most directly associated with star-formation. We propose a joint interdisciplinary observational/theoretical DIP program in Astrophysics for study of high-redshift galaxy and ISM evolution. Our program will be based on our already started and upcoming surveys, PHIBBS2 and ALMA-SFG for mm-wave spectroscopy at the advanced ground-based IRAM/NOEMA and ALMA interferometric arrays, in combination with near-IR KMOS3D with the ESO-VLT, to be followed by next-generation JWST observations from space. DIP/DFG funding will be used primarily for support of fundamental theory, development of analytic modeling tools and simulations. Key questions include: When and how did the (blue) SFG "main-sequence" become established? What determines the maximal "quenching mass" for star-forming galaxies? Is this due to shutdown of accretion from the surrounding hot medium and conversion to molecular gas? Or does internally generated feedback in the form of stellar or AGN wind-driven molecular/ionized outflows halt the galaxy growth rates? What are the star-forming and gaseous properties of galaxies transitioning to the (red) quiescent mode. How is angular momentum transferred from the galaxy halos to the stellar and gaseous disks? Does heavy element abundance ("metallicity") influence the star-formation efficiencies? Our theory and modeling work in coordination with our observing programs will be based on a series of work-packages especially designed with the training of young scientists in mind - undergrads, MSc/diploma, PhD students, and postdocs - bringing together a team of experts from the German and Israeli sides. Our research program will build on the established and internationally recognized German-Israel Astrophysics collaboration, led by the Genzel & Sternberg MPE-TAU partnership, for a major broadening of our research moving forward.